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Abstract:

A diesel fuel formulation is disclosed containing a water-in-fuel emulsion
of (a) a Fischer-Tropsch derived gas oil, optionally in combination with
conventional diesel, (b) a fatty acid alkyl ester in an amount of at
least 1% v/v and (c) water. An emulsifier may be present.
Formulations have useful emissions properties and retain performance
characteristics in spite of the presence of water.
Methods of preparing the formulations and their uses are also described.

Claims:

1. A diesel fuel formulation comprising a water-in-fuel emulsion of (a) a
Fischer-Tropsch derived gas oil, (b) a fatty acid alkyl ester in an
amount of at least 1% v/v and (c) water.

2. The diesel fuel formulation of claim 1 further comprising an
emulsifier.

4. The diesel fuel of claim 1 where the water is present in an amount of
1% v/v or greater.

5. The diesel fuel of claim 4 further comprising an emulsifier.

6. The diesel fuel of claim 5 wherein the emulsifier is present in an
amount of 0.1% v/v or greater.

7. A method for preparing a diesel fuel formulation comprising blending
together, with agitation, the components comprising (a) a Fischer-Tropsch
derived gas oil, (b) a fatty acid alkyl ester in an amount of at least 1%
v/v and (c) water so as to form a water-in-fuel emulsion.

8. A kit for preparing a diesel fuel formulation comprising a combination
of at least two members selected from the group consisting of (i) a
Fischer-Tropsch derived gas oil, (ii) a fatty acid alkyl ester and (iii)
an emulsifier.

9. The kit of claim 8 wherein two or more members of the combination are
combined in a pre-mix and/or the kit is combined with an apparatus for
forming an emulsion.

10. A method of operating a fuel consuming system, which method comprises
introducing into the system a fuel formulation of claim 1.

11. A vehicle emissions control system comprising an engine adapted to run
on a formulation of claim 1, and an exhaust after-treatment device
adapted to remove emissions obtained from combustion of said formulation
in the engine.

Description:

[0002]The present invention relates to diesel fuel formulations and their
preparation and use, as well as pre-mixes used to form these, as well as
vehicle emission control systems which utilise them.

BACKGROUND OF THE INVENTION

[0003]Emulsions of water can be formed in hydrocarbon fuels. In the case
of diesel fuels such as automotive gas oils, such emulsions have been
shown to reduce levels of emissions on combustion, in particular reducing
nitrogen oxide (NOx) and particulate matter (PM) emissions (see for
example Y. Yoshimito et al. SAE Paper 982490, (1998); Barnaud et al. SAE
Paper 2000-01-1861 (2000) and WO-A-99/13028.

[0004]Diesel fuel formulations can include the reaction products of
Fischer-Tropsch condensation processes, for example, such as the process
known as Shell Middle Distillate Synthesis (van der Burgt et al, "The
Shell Middle Distillate Synthesis Process", paper delivered at the 5th
Synfuels Worldwide Symposium, Washington D.C., November 1985; see also
the November 1989 publication of the same title from Shell International
Petroleum Company Ltd, London, UK). In particular, automotive diesel fuel
compositions can include Fischer-Tropsch derived gas oils often in blends
with other diesel base fuels such as petroleum derived gas oils.

[0005]The benefits of Fischer-Tropsch derived fuels, as compared to their
petroleum derived counterparts, include their relatively high cetane
numbers, their relatively low emissions on combustion, for example in an
engine, and their typically low levels of undesirable fuel components
such as sulphur, nitrogen and aromatics.

[0006]When an emulsion is formed between water and a Fischer-Tropsch
derived fuel, again improvements in emissions levels have been found to
result, as shown in U.S. Pat. No. 7,229,481. Here it was also found that
Fischer-Tropsch fuels, having typically higher cetane numbers than
conventional petroleum derived fuels, can help to compensate for the
cetane number lowering effect of the water. This in turn can help to
reduce problems such as impaired engine performance and noise, which are
potentially associated with reduced cetane number. It can also allow the
use of lower levels of ignition improving additives in the water/fuel
mixtures.

[0007]Biofuels such as rapeseed methyl ester (RME) and other fatty acid
alkyl esters (FAAEs) have been included in diesel fuel blends in order to
reduce life cycle greenhouse gas emissions and restore lubricity, in
particular to fuels which have been subjected to high levels of
hydrotreatment to reduce sulphur levels. There may be environmental
reasons why the use of biofuels is particularly preferred in some
instances. They are, however, known to increase the density of the blend
with respect to the base fuel and can increase tailpipe nitrogen oxide
(NOx) emissions.

[0008]WO-A-2004/035713 describes the use of these and other oxygenates in
ternary fuel blends which mimic the properties of the base fuel, and give
overall improved performance.

[0009]However, oxygenates of this type are generally polar in nature. As a
result, they would be expected to alter the polarity of the diesel phase
of a diesel-water system, thus making emulsions of the type described in
U.S. Pat. No. 7,229,481 difficult to make and unstable once formed.

SUMMARY OF THE INVENTION

[0010]A diesel fuel formulation is provided comprising a water-in-fuel
emulsion of (a) a Fischer-Tropsch derived gas oil, (b) a fatty acid alkyl
ester in an amount of at least 1% v/v and (c) water. A method for
preparing such formulation, and a kit for preparing such formulation is
also provided. A method of operating a fuel consuming system is also
provided.

DETAILED DESCRIPTION OF THE INVENTION

[0011]The applicants have found, that in so far as even relatively high
levels of oxygenates may be included and thus be useful fuel components,
without reducing stability to an impractical extent.

[0012]According to one embodiment of the present invention there is
provided a diesel fuel formulation containing a water-in-fuel emulsion of
(a) a Fischer-Tropsch derived gas oil, (b) a fatty acid alkyl ester in an
amount of at least 1% v/v and (c) water.

[0013]In a particular embodiment, the formulation further contains an
emulsifier.

[0014]The applicants have found that emulsions comprising 1% v/v or more
of fatty acid alkyl ester may be formed without difficulty. Furthermore,
they have been found to be stable for significant periods of time, thus
allowing them to be used in practical situations. As a result,
formulations with significant advantages may be formed.

[0015]In particular, the formulations have good performance, and may
remain on specification in spite of the presence of water in relatively
high amounts, as a result of the inclusion of Fischer-Tropsch derived gas
oils, and also fatty acid alkyl esters to some extent. These have a high
cetane number, which therefore counteracts any reduction in cetane number
produced as a result of the addition of water. (Water in diesel is known
to lower the cetane number potentially giving problematic combustion
performance and noise.)

[0016]Furthermore, the formulations may give rise to reduced nitrogen
oxide (NOx) or particulate matter (PM) emissions in some circumstances.
This is because any increase in NOx emissions as a result of the presence
of fatty acid alkyl esters is countered by the presence of
Fischer-Tropsch derived gas oil and water in the formulation.
Furthermore, the fatty acid alkyl esters themselves will produce less PM
emissions and black smoke.

[0017]In addition, the inclusion of water means that the formulations are
cost effective to produce.

[0018]In a formulation according to the present invention, the
concentration of the fatty acid alkyl ester (b) may be 1% v/v or greater,
for example 1.2% v/v or greater or 1.5% v/v or greater, for instance 2%
v/v or greater or even 3% v/v or greater or 5% v/v or greater or 7% v/v
or greater. It may be up to 30% v/v, for example up to 20% v/v or
preferably up to 10% v/v. A suitable concentration may be from 1 to 30%
v/v, such as from 1.2 to 20% v/v or from 5 to 10% v/v.

[0019]In a formulation according to the present invention, the
concentration of water may be 1% v/v or greater, for example 5% v/v or
greater, such as 10% v/v or greater. It may be up to 35% v/v, for example
up to 30% v/v or 25% v/v. A suitable concentration may be from 1 to 35%
v/v or from 1 to 30% v/v, for instance from 5 to 25% v/v.

[0020]Where an emulsifier is present, its concentration in the formulation
may be 0.1% v/v or greater, for example 0.5% v/v or greater. It may be up
to 10% v/v, for example up to 5% v/v. A suitable concentration may be
from 0.1 to 10% v/v or from 0.5 to 5% v/v.

[0021]In some embodiments, the Fischer-Tropsch derived gas oil will
constitute the balance or substantial balance of the formulation,
depending upon whether other additives, for example as described below,
are present in the formulation. However, in a particular embodiment, the
formulation will contain conventional, petroleum derived, diesel as well
as the Fischer-Tropsch derived gas oil, and these two components together
will make up the balance of the formulation.

[0022]Typically in a formulation according to the present invention, the
concentration of the Fischer-Tropsch derived gas oil (a) may be 0.5% v/v
or greater. It may be up to 98% v/v, for example up to 90% v/v such as up
to 85% v/v. A suitable concentration may be from 0.5% to 99% v/v or from
0.5% to 90% v/v, for example from 0.5% to 85% v/v.

[0023]Where present, conventional diesel is suitably present in a
formulation according to the present invention, at a concentration of
0.5% v/v or greater. It may be up to 85% v/v, for example up to 75% v/v.
A suitable concentration may be from 0.5% v/v to 85% v/v or from 0.5% v/v
to 75% v/v, for instance from 0.5% v/v to 50% v/v.

[0024]The water-in-fuel emulsion may be prepared using conventional
emulsion preparation techniques, typically by blending together, with
agitation, the components (a), (b) and (c), and optionally also
conventional diesel, suitably with an emulsifier. In particular,
components (a) and (b) are mixed together with any conventional diesel
fuel and emulsifier used with rapid stirring using a device such as a
high shear mixer, for instance a Silverson high shear laboratory mixer.
Component (c), water, is then added gradually, at a rate suitable to give
rise to an emulsion bearing in mind the speed of stirring, etc. For
example, the water may be added dropwise, whilst stirring is carried out.
Stirring is continued after completion of the addition, for example for a
period of 1 to 5 minutes to ensure that mixing is complete. The procedure
is conveniently carried out at room temperature, pressure and humidity.

[0025]Processes of this type form another aspect of the present invention.

[0026]Diesel emulsions of the type which form the subject of the present
invention are generally blended and then used as an automotive fuel
immediately or within a few days, for example up to 5 days, and
preferably up to 2 days, of preparation. In order to achieve this, the
components or pre-mixes of one or more of the components are delivered to
a site, such as a transport distribution or public transport depot, and
mixed using a suitable stirring device on site, ready for use.

[0027]As such, a kit comprising a combination of at least two members
selected from the group consisting of (i) component (a) above, (ii)
component (b) above and (iii) an emulsifier forms a third aspect of the
present invention. Suitably the kit comprises all three of (i), (ii) and
(iii). It may optionally further comprise conventional diesel if required
in the formulation. Water, in particular deionised water suitable as
component (c), may also be supplied with the kit if required, although
this may be sourced separately. The relative amounts of the components of
the kit are selected so that they may form a formulation of the present
invention as described above. The kit may be accompanied by a set of
instructions to allow the components to be mixed together and formed into
an emulsion. Apparatus suitable for forming the emulsion, in particular a
high shear mixer, may also be supplied and thus a combination of such an
apparatus and a kit as described above may form a fourth aspect of the
present invention.

[0028]If required, pre-mixes comprising two or more components (i), (ii)
or (iii), as well as any conventional diesel required for formation of a
formulation of the present invention, may suitably be provided, for
example as an element of a kit as described above.

[0029]Thus, another aspect of the present invention provides a diesel fuel
formulation pre-mix which comprises at least two of (a) a Fischer-Tropsch
derived gas oil and (b) a fatty acid alkyl ester in an amount so that it
comprises at least 1% v/v in a diesel fuel formulation prepared
therefrom, and an emulsifier. The pre-mix may further contain
conventional diesel where this is required in the final formulation.
Emulsifiers are suitably present in an amount such that they comprise
from 0.1 to 10% v/v of the final formulation, once the water has been
added.

[0030]By "Fischer-Tropsch derived" is meant that a fuel is, or derives
from, a synthesis product of a Fischer-Tropsch condensation process. A
Fischer-Tropsch derived fuel may also be referred to as a GTL
(Gas-to-Liquid) fuel. The term "non-Fischer-Tropsch derived" may be
construed accordingly.

[0031]Fischer-Tropsch derived fuels are known and in use in for instance
automotive diesel fuel compositions, and are described in more detail
below. They tend to contain low levels of aromatic fuel components and of
sulphur and other polar species, and to have relatively high cetane
numbers when compared to their mineral derived counterparts.

in the presence of an appropriate catalyst and typically at elevated
temperatures (e.g. 125 to 300° C., preferably 175 to 250°
C.) and/or pressures (e.g. 5 to 100 bar, preferably 12 to 50 bar).
Hydrogen:carbon monoxide ratios other than 2:1 may be employed if
desired.

[0033]The carbon monoxide and hydrogen may themselves be derived from
organic or inorganic, natural or synthetic sources, typically either from
natural gas or from organically derived methane. The gases which are
converted into liquid fuel components using such processes can in general
include natural gas (methane), LPG (e.g. propane or butane),
"condensates" such as ethane, synthesis gas (CO/hydrogen) and gaseous
products derived from coal, biomass and other hydrocarbons.

[0034]Gas oil products may be obtained directly from the Fischer-Tropsch
reaction, or indirectly for instance by fractionation of Fischer-Tropsch
synthesis products or from hydrotreated Fischer-Tropsch synthesis
products. Hydrotreatment can involve hydrocracking to adjust the boiling
range (see, e.g. GB-B-2077289 and EP-A-0147873) and/or hydroisomerisation
which can improve cold flow properties by increasing the proportion of
branched paraffins. EP-A-0583836 describes a two step hydrotreatment
process in which a Fischer-Tropsch synthesis product is firstly subjected
to hydroconversion under conditions such that it undergoes substantially
no isomerisation or hydrocracking (this hydrogenates the olefinic and
oxygen-containing components), and then at least part of the resultant
product is hydroconverted under conditions such that hydrocracking and
isomerisation occur to yield a substantially paraffinic hydrocarbon fuel.
The desired gas oil fraction(s) may subsequently be isolated for instance
by distillation.

[0035]Other post-synthesis treatments, such as polymerisation, alkylation,
distillation, cracking-decarboxylation, isomerisation and hydroreforming,
may be employed to modify the properties of Fischer-Tropsch condensation
products, as described for instance in U.S. Pat. No. 4,125,566 and U.S.
Pat. No. 4,478,955.

[0036]Typical catalysts for the Fischer-Tropsch synthesis of paraffinic
hydrocarbons comprise, as the catalytically active component, a metal
from Group VIII of the periodic table, in particular ruthenium, iron,
cobalt or nickel. Suitable such catalysts are described for instance in
EP-A-0583836 (pages 3 and 4).

[0037]An example of a Fischer-Tropsch based process is the SMDS (Shell
Middle Distillate Synthesis) described by van der Burgt et al in "The
Shell Middle Distillate Synthesis Process", paper delivered at the 5th
Synfuels Worldwide Symposium, Washington D.C., November 1985 (see also
the November 1989 publication of the same title from Shell International
Petroleum Company Ltd, London, UK). This process (also sometimes referred
to as the Shell "Gas-To-Liquids" or "GTL" technology) produces middle
distillate range products by conversion of a natural gas (primarily
methane) derived synthesis gas into a heavy long chain hydrocarbon
(paraffin) wax which can then be hydroconverted and fractionated to
produce liquid transport fuels such as the gas oils useable in diesel
fuel compositions. A version of the SMDS process, utilising a fixed bed
reactor for the catalytic conversion step, is currently in use in
Bintulu, Malaysia and its gas oil products have been blended with
petroleum derived gas oils in commercially available automotive fuels.

[0038]Gas oils prepared by the SMDS process are commercially available for
instance from Shell companies. Further examples of Fischer-Tropsch
derived gas oils are described in EP-A-0583836, EP-A-1101813,
WO-A-97/14768, WO-A-97/14769, WO-A-00/20534, WO-A-00/20535,
WO-A-00/11116, WO-A-00/11117, WO-A-01/83406, WO-A-01/83641,
WO-A-01/83647, WO-A-01/83648 and U.S. Pat. No. 6,204,426.

[0039]By virtue of the Fischer-Tropsch process, a Fischer-Tropsch derived
fuel has essentially no, or undetectable levels of, sulphur and nitrogen.
Compounds containing these heteroatoms tend to act as poisons for
Fischer-Tropsch catalysts and are therefore removed from the synthesis
gas feed. Fischer-Tropsch derived fuels are known to give rise to reduced
levels of emissions (in particular NOx and particulate matter emissions)
compared to their petroleum derived counterparts.

[0040]Further, the Fischer-Tropsch process as usually operated produces no
or virtually no aromatic components. The aromatics content of a
Fischer-Tropsch derived fuel, suitably determined by ASTM D4629, will
typically be below 1% w/w, preferably below 0.5% w/w and more preferably
below 0.2 or 0.1% w/w.

[0041]Generally speaking, Fischer-Tropsch derived fuels have relatively
low levels of polar components, in particular polar surfactants, for
instance compared to petroleum derived fuels. Such polar components may
include for example oxygenates, and sulphur- and nitrogen-containing
compounds. A low level of sulphur in a Fischer-Tropsch derived fuel is
generally indicative of low levels of both oxygenates and
nitrogen-containing compounds, since all are removed by the same
treatment processes.

[0042]A Fischer-Tropsch derived gas oil should be suitable for use as a
diesel fuel, ideally as an automotive diesel fuel; its components (or the
majority, for instance 95% v/v or greater, thereof) should therefore have
boiling points within the typical diesel fuel ("gas oil") range, i.e.
from about 150 to 400° C. or from 170 to 370° C. It will
suitably have a 90% v/v distillation temperature of from 300 to
370° C.

[0043]A Fischer-Tropsch derived gas oil will typically have a density from
0.76 to 0.79 g/cm3 at 15° C.; a cetane number (ASTM D613)
greater than 70, suitably from 74 to 85; a kinematic viscosity (ASTM
D445) from 2 to 4.5, preferably from 2.5 to 4.0, more preferably from 2.9
to 3.7, mm2/s at 40° C.; and a sulphur content (ASTM D2622)
of 5 mg/kg or less, preferably of 2 mg/kg or less.

[0044]Preferably a Fischer-Tropsch derived gas oil used in the present
invention is a product prepared by a Fischer-Tropsch methane condensation
reaction using a hydrogen/carbon monoxide ratio of less than 2.5,
preferably less than 1.75, more preferably from 0.4 to 1.5, and ideally
using a cobalt containing catalyst. Suitably it will have been obtained
from a hydrocracked Fischer-Tropsch synthesis product (for instance as
described in GB-B-2077289 and/or EP-A-0147873), or more preferably a
product from a two-stage hydroconversion process such as that described
in EP-A-0583836 (see above). In the latter case, preferred features of
the hydroconversion process may be as disclosed at pages 4 to 6, and in
the examples, of EP-A-0583836.

[0045]Suitably a Fischer-Tropsch derived gas oil used in the present
invention is a product prepared by a low temperature Fischer-Tropsch
process, by which is meant a process operated at a temperature of
250° C. or lower, such as from 125 to 250° C. or from 175
to 250° C., as opposed to a high temperature Fischer-Tropsch
process which might typically be operated at a temperature of from 300 to
350° C.

[0046]Suitably, in accordance with the present invention, a
Fischer-Tropsch derived gas oil will consist of at least 70% w/w,
preferably at least 80% w/w, more preferably at least 90 or 95 or 98%
w/w, most preferably at least 99 or 99.5 or even 99.8% w/w, of paraffinic
components, preferably iso- and normal paraffins. The weight ratio of
iso-paraffins to normal paraffins will suitably be greater than 0.3 and
may be up to 12; suitably it is from 2 to 6. The actual value for this
ratio will be determined, in part, by the hydroconversion process used to
prepare the gas oil from the Fischer-Tropsch synthesis product.

[0048]According to the present invention, a mixture of two or more
Fischer-Tropsch derived gas oils may be used in the fuel formulation.

[0049]Suitably, the fatty acid alkyl ester is derived from organic
material, as in the case of currently available "biofuels" such as
vegetable oils and their derivatives--the use of such components in fuel
formulations is becoming increasingly desirable, due to both
environmental and associated legislative constraints, and can bring its
own advantages. Biofuels such as rapeseed methyl ester (RME) have for
example been included in diesel fuel blends in order to reduce life cycle
greenhouse gas emissions and restore lubricity in particular to fuels
which have been subjected to high levels of hydrotreatment to reduce
sulphur levels.

[0050]Fatty acid alkyl esters (b), of which the most commonly used in the
present context are the methyl esters, are already known as renewable
diesel fuels (so-called "biodiesel" fuels). They contain long chain
carboxylic groups (generally from 10 to 22 carbon atoms long), each
having an alcohol-derived alkyl group attached to one end. Organically
derived oils such as vegetable oils (including recycled vegetable oils)
and animal fats can be subjected to a transesterification process with an
alcohol (typically a C1 to C5 alcohol) to form the
corresponding fatty esters, typically mono-alkylated. This process, which
is suitably either acid- or base-catalysed such as with the base KOH,
converts the triglycerides contained in the oils into fatty acid esters
and free glycerol, by separating the fatty acid components of the oils
from their glycerol backbone.

[0051]In accordance with the present invention, a fatty acid alkyl ester
may be derived from any alkylated fatty acid or mixture of fatty acids.
Its fatty acid component(s) are preferably derived from a biological
source, more preferably a vegetable source. They may be saturated or
unsaturated; if the latter, they may have one or more double bonds. They
may be branched or un-branched. Suitably, they will have from 10 to 30,
more suitably from 10 to 22 or from 12 to 22, carbon atoms in addition to
the acid group(s) --CO2H. A fatty acid alkyl ester will typically
comprise a mixture of different fatty acid esters of different chain
lengths, depending on its source. For instance the commonly available
rapeseed oil contains mixtures of palmitic acid (C16), stearic acid
(C18), oleic, linoleic and linolenic acids (C18, with one, two
and three unsaturated carbon-carbon bonds respectively) and sometimes
also erucic acid (C22)--of these the oleic and linoleic acids form
the major proportion. Soybean oil contains a mixture of palmitic,
stearic, oleic, linoleic and linolenic acids. Palm oil usually contains a
mixture of palmitic, stearic and linoleic acid components.

[0053]Such a fatty acid alkyl ester is preferably a C1 to C5
alkyl ester, more preferably a methyl, ethyl or propyl (suitably
iso-propyl) ester, yet more preferably a methyl or ethyl ester and in
particular a methyl ester.

[0054]A fatty acid alkyl ester may for example be selected from the group
consisting of rapeseed methyl ester (RME, also known as rape oil methyl
ester or rape methyl ester), soy methyl ester (SME, also known as soybean
methyl ester), palm oil methyl ester (POME), coconut methyl ester (CME)
(in particular unrefined CME; the refined product is based on the crude
but with some of the higher and lower alkyl chains (typically the
C6, C8, C10, C16 and C18) components removed)
and mixtures thereof. In general, it may be either natural or synthetic,
refined or unrefined ("crude").

[0055]The fatty acid alkyl ester (b) will typically be a liquid at ambient
temperature, with a boiling point preferably from 100 to 360° C.,
more preferably from 250 to 290° C. Its density is suitably from
0.75 to 0.9 g/cm3 at 15° C. (ASTM D4502/IP 365), and its
flash point greater than 55° C.

[0056]A fuel formulation according to the invention may contain a mixture
of two or more fatty acid alkyl esters, for instance selected from those
described above.

[0057]Suitable emulsifiers for use in the formulation of the present
invention include surfactants. They may be ionic or non-ionic
surfactants, in particular non-ionic surfactants. Suitable non-ionic
surfactants include alkoxylates such as alcohol ethoxylates and
alkylphenol ethoxylates; carboxylic acid esters, such as glycerol esters
and polyoxyethylene esters; anhydrosorbitol esters, such as ethoxylated
anhydrosorbitol esters; natural ethoxylated fats, oils and waxes; glycol
esters of fatty acids; alkyl polyglycosides; carboxylic amides, such as
diethanolamine condensates and monoalkanolamine condensates; fatty acid
glucamides; polyalkylene oxide block copolymers and
poly(oxyethylene-co-oxypropylene) non-ionic surfactants.

[0058]In a particular embodiment, a mixture of surfactants is used. It is
preferred that the HLB (hydrophile-lipophile balance) value of the
surfactant or mixture of surfactants is in the range 3 to 9, more
preferably 3 to 6. In the case of a mixture of surfactants, the HLB of
the mixture is dependent on the proportions of the surfactants in the
mixture and their respective HLB values, and is preferably in the ranges
given above.

[0060]A particularly suitable mixture comprises TWEEN 21 and SPAN 80 but
mixtures may comprise any of the surfactants listed above.

[0061]Where present in the formulation of the present invention, the
"conventional diesel" will comprise a diesel base fuel such as an
automotive gas oil (AGO). Typical diesel fuel components comprise liquid
hydrocarbon middle distillate fuel oils, for instance petroleum derived
gas oils. Such base fuel components may be organically or synthetically
derived. They will typically have boiling points within the usual diesel
range of 125 or 150 to 400 or 550° C., depending on grade and use.
They will typically have densities from 0.75 to 1.0 g/cm3,
preferably from 0.8 to 0.9 or 0.86 g/cm3, at 15° C. (IP 365)
and measured cetane numbers (ASTM D613) of from 35 to 80, more preferably
from 40 to 75 or 70. Their initial boiling points will suitably be in the
range 150 to 230° C. and their final boiling points in the range
290 to 400° C. Their kinematic viscosity at 40° C. (ASTM
D445) might suitably be from 1.5 to 4.5 mm2/s.

[0062]Such fuels are generally suitable for use in a compression ignition
(diesel) internal combustion engine, of either the indirect or direct
injection type.

[0063]A fuel formulation according to the present invention may be
suitable for use in a compression ignition (diesel) internal combustion
engine, of either the indirect or direct injection type.

[0064]Such a diesel fuel formulation will suitably comply with applicable
current standard specification(s) such as for example EN 590:2004 (for
Europe) or ASTM D-975-06 (for the USA). By way of example, the
formulation may have a density (EN ISO 12185) from 0.82 to 0.845
g/cm3 at 15° C.; a 95% recovered temperature (EN ISO 3405) of
360° C. or less; a cetane number (EN ISO 5165) of 51 or greater; a
kinematic viscosity (EN ISO 3104) from 2 to 4.5 centistokes at 40°
C.; a sulphur content (EN ISO 20847) of 50 ppmw or less; and/or a
polyaromatics content (EN 12916) of less than 11%. Relevant
specifications may, however, differ from country to country and from year
to year and may depend on the intended use of the fuel composition.

[0065]A formulation according to the present invention is suitably stable
for at least 12 hours following its preparation. It may be stable for at
least 24 or 36 or 48 or 60 hours following its preparation. By "stable"
is meant that, when the formulation is left to stand undisturbed, the
organic and aqueous phases of the water-in-fuel emulsion do not visibly
separate.

[0066]A fuel formulation according to the present invention may contain
other components in addition to the Fischer-Tropsch derived gas oil, the
fatty acid alkyl ester and the water. It may in particular include one or
more diesel fuel additives. Many such additives are known and readily
available.

[0067]The total additive content in the fuel formulation may suitably be
from 50 to 10000 mg/kg, preferably below 5000 mg/kg.

[0068]Further additives which are often included in diesel fuel
formulations are cetane improvers (also known as an ignition improvers).
As a result of carrying out the present invention, however, lower levels
of such additives may be needed as the presence of the Fischer-Tropsch
derived gas oil can itself serve to increase the cetane number of the
overall formulation, even in the presence of the normally cetane-lowering
water. The oxygenate may also contribute to maintaining the cetane
number.

[0069]Thus, according to another aspect of the present invention, there is
provided a combination of a Fischer-Tropsch derived gas oil and a fatty
acid alkyl ester in an emulsified diesel fuel formulation, that reduces
the concentration of an additive selected from an ignition improving
additive or lubricity enhancing additive in the formulation.

[0070]The ignition improving additive may be any suitable ignition
improver. Many such additives are known and commercially available, and
may also be known (in the context of diesel fuels) as "cetane improvers"
or "cetane number improvers"; they typically function by increasing the
concentration of free radicals in a fuel formulation. The ignition
improver may in particular be a diesel fuel ignition improver, i.e. an
ignition improving agent suitable for use in a diesel fuel formulation.

[0071]An ignition improver may for example be selected from:

[0072]a) organic nitrates of the general formula R1--O--NO2, or
nitrites of the general formula R1--O--NO, where R1 is a
hydrocarbyl group such as in particular an alkyl, cycloalkyl, alkenyl or
aromatic group, or an ether containing group, preferably having from 1 to
10, more preferably from 1 to 8 or from 1 to 6 or from 1 to 4, carbon
atoms;

[0073]b) organic peroxides and hydroperoxides, of the general formula
R2--O--O--R3, where R2 and R3 are each independently
either hydrogen or a hydrocarbyl group such as in particular an alkyl,
cycloalkyl, alkenyl or aromatic group, preferably having from 1 to 10,
more preferably from 1 to 8 or from 1 to 6 or from 1 to 4, carbon atoms
(provided that R2 and R3 are not both hydrogen); and

[0074]c) organic peracids and peresters, of the general formula
R4--C(O)--O--O--R5, where R4 and R5 are each
independently either hydrogen or a hydrocarbyl group such as in
particular an alkyl, cycloalkyl, alkenyl or aromatic group, preferably
having from 1 to 10, more preferably from 1 to 8 or from 1 to 6, such as
from 1 to 4, carbon atoms.

[0075]Examples of ignition improvers of type (a) include (cyclo)alkyl
nitrates such as isopropyl nitrate, 2-ethylhexyl nitrate (2-EHN) and
cyclohexyl nitrate, and ethyl nitrates such as methoxyethyl nitrate.
Examples of type (b) include di-tert-butyl peroxide.

[0076]Other diesel fuel ignition improvers are disclosed in U.S. Pat. No.
4,208,190 at column 2, line 27 to column 3, line 21.

[0077]In particular, the ignition improver may be selected from
(cyclo)alkyl nitrates such as 2-ethylhexyl nitrate (2-EHN), dialkyl
peroxides such as di-tert-butyl peroxide, and mixtures thereof. It may in
particular be a (cyclo)alkyl nitrate such as 2-EHN.

[0078]Diesel fuel ignition improvers are commercially available for
instance as HITECT® 4103 (ex. Afton Chemical) and as CI-0801 and
CI-0806 (ex. Innospec Inc.).

[0079]Lubricity enhancing additives used in conventional fuel compositions
may be any additive capable of improving the lubricity of a fuel
composition and/or of imparting anti-wear effects when the composition is
in use in an engine or other fuel-consuming system.

[0080]The lubricity enhancing additive may contain, typically as active
constituent(s), one or more carboxylic acids. Suitable carboxylic acids
include fatty acids and aromatic acids, in particular fatty acids such as
those listed below. A lubricity enhancing additive may alternatively be
based on non-acid actives such as esters or amides. Preferably the
lubricity enhancing additive is ester- or amide-based, more preferably
ester-based.

[0081]Suitable esters for use in such additives are carboxylic acid
esters, in particular those derived from fatty acids, and mixtures
thereof. Such fatty acids may be saturated or unsaturated (which includes
polyunsaturated). They may for example contain from 1 or 2 to 30 carbon
atoms, suitably from 10 to 22 carbon atoms, preferably from 12 to 22 or
from 14 to 20 carbon atoms, more preferably from 16 to 18 carbon atoms
and most preferably 18 carbon atoms. Examples include oleic acid,
linoleic acid, linolenic acid, linolic acid, stearic acid, palmitic acid
and myristic acid. Of these, oleic, linoleic and linolenic acids may be
preferred, more preferably oleic and linoleic acids. In one embodiment of
the present invention, the lubricity enhancing additive is a derivative
(in particular an ester) of tall oil fatty acid, which is derived from
tall oil and contains mostly fatty acids (such as oleic and linoleic)
with a small proportion of rosin acids.

[0082]Lubricity enhancing additives based on ester-functionalised
oligomers or polymers (e.g. olefin oligomers) may also be of use. Such
esters may be mono-alcohol esters such as methyl esters, or more suitably
may be polyol esters such as glycerol esters. Most preferred is a mono-,
di- or tri-glyceride of a fatty acid, or conveniently a mixture of two or
more such species.

[0083]Suitable amides for use in such additives are fatty acid amides,
wherein preferred fatty acids may be as described above, for example
fatty acid amides of mono- or in particular di-alkanolamines such as
diethanolamine.

[0088]WO-A-94/17160--certain esters of a carboxylic acid and an alcohol
wherein the acid has from 2 to 50 carbon atoms and the alcohol has 1 or
more carbon atoms, particularly glycerol monooleate and di-isodecyl
adipate, as fuel additives for wear reduction in a diesel engine
injection system;

[0090]WO-A-98/01516--certain alkyl aromatic compounds having at least one
carboxyl group attached to their aromatic nuclei, to confer anti-wear
lubricity effects particularly in low sulphur diesel fuels.

[0091]A lubricity enhancing additive may contain other ingredients in
addition to the key lubricity enhancing active(s), for example a dehazer
and/or an anti-rust agent, as well as conventional solvent(s) and/or
excipient(s). Alternatively, a lubricity enhancing additive may consist
essentially or even entirely of a lubricity enhancing active, or mixture
thereof, of the type described above.

[0092]In the context of the above aspect of the present invention, the
term "reducing" embraces any degree of reduction--for instance 5% or more
of the original additive concentration, preferably 10 or 20% or more.

[0093]The reduction may be as compared to the concentration of the
relevant additive which would otherwise have been incorporated into the
formulation in order to achieve the properties and performance required
or desired of it in the context of its intended use. This may for
instance be the concentration of the additive which was present in the
formulation prior to the realisation that a combination of a
Fischer-Tropsch derived gas oil and an oxygenate could be used in the way
provided by the present invention, or which was present in an otherwise
analogous formulation intended (e.g. marketed) for use in an analogous
context, prior to adding a combination of a Fischer-Tropsch derived gas
oil and an oxygenate to it.

[0094]Thus, (active matter) concentration of the ignition improver in a
fuel formulation prepared according to the present invention may be 3000
ppmw or less, preferably 1000 ppmw or less, for example from 5 to 50
ppmw. The formulation may contain no or substantially no ignition
improving additives.

[0095]The (active matter) concentration of the lubricity enhancing
additive used in a fuel composition according to the present invention
may be 1000 ppmw or less, preferably 500 ppmw or less, more preferably
400 or 300 ppmw or less. Its (active matter) concentration will suitably
be 100 ppmw or less, preferably 50 or 30 ppm or less. In the case of any
lubricity enhancing additives, these may in fact be reduced to zero as a
result of the use of the formulations of the first aspect of the present
invention.

[0096]According to yet another aspect, the present invention provides a
combination of a Fischer-Tropsch derived gas oil and oxygenate in an
emulsified diesel fuel formulation, that improves the emissions
performance of the formulation.

[0097]By "emissions performance" is meant the amount of combustion-related
emissions (such as particulates, nitrogen oxides, carbon monoxides and
gaseous (unburned) hydrocarbons and carbon dioxide) generated by a fuel
consuming system (typically an engine such as a diesel engine) running on
the relevant fuel formulation. In the context of the present invention,
emissions of particulates and/or of nitrogen oxides NOx as well as black
smoke, are of particular interest.

[0098]Thus, in general, an improvement in emissions performance may be
manifested by a reduced level of combustion-related emissions when the
fuel formulation is used in a fuel consuming system.

[0099]Emission levels may be measured using standard testing procedures
such as the European R49, ESC, OICA or ETC for (for heavy-duty engines)
or ECE+EUDC or MVEG (for light-duty engines) test cycles. Ideally
emissions performance is measured on a diesel engine built to comply with
the Euro II standard emissions limits (1996) or with the Euro III (2000),
IV (2005) or even V (2008) standard limits. A heavy-duty engine is
particularly suitable for this purpose. Gaseous and particle emissions
may be determined using for instance a Horiba Mexa® 9100 gas
measurement system and an AVL Smart Sampler® respectively.

[0100]In the context of the above aspect of the present invention,
"improving" the emissions performance of the fuel formulation embraces
any degree of improvement compared to the emissions performance of the
formulation before the oxygenate is incorporated. This may, for example,
involve adjusting the emissions performance of the formulation, by means
of the oxygenate, in order to meet a desired target. For example, the
precise amount of the oxygenate may be varied, or the precise chemical
nature of the oxygenate may be varied in order to achieve the desired
target.

[0101]In particular, as a result of the inclusion of Fischer-Tropsch
derived gas oil in the formulation of the present invention, the cetane
number of the formulation may be maintained.

[0102]The cetane number of a fuel formulation may be determined in known
manner, for instance using the standard test procedure ASTM D613 (ISO
5165, IP 41) which provides a so-called "measured" cetane number obtained
under engine running conditions.

[0103]More preferably, the cetane number may be determined using the more
recent and precise "ignition quality test" (IQT) (ASTM D6890, IP 498),
which provides a "derived" cetane number based on the time delay between
injection and combustion of a fuel sample introduced into a constant
volume combustion chamber. This relatively rapid technique can be used on
laboratory scale (ca 100 ml) samples of a range of different fuels.

[0104]Alternatively, cetane number may be measured by near infrared
spectroscopy (NIR), as for example described in U.S. Pat. No. 5,349,188.
This method may be preferred in a refinery environment as it can be less
cumbersome than for instance ASTM D613. NIR measurements make use of a
correlation between the measured spectrum and the actual cetane number of
a sample. An underlying model is prepared by correlating the known cetane
numbers of a variety of fuel samples with their near infrared spectral
data.

[0105]The present invention may result in a fuel formulation which has a
derived cetane number (IP 498) of 40 or greater, or of 50 or greater, or
of 60 or greater.

[0106]In the context of the present invention, use of a combination of a
Fischer-Tropsch derived gas oil and an oxygenate in a fuel formulation
means incorporating these elements into the formulation, typically as a
blend (i.e. a physical mixture) with one or more other fuel components.
The blend will conveniently be incorporated before the formulation is
emulsified and introduced into an engine or other system which is to be
run on the formulation. Instead or in addition the use of a combination
of a Fischer-Tropsch derived gas oil and an oxygenate may involve running
a fuel-consuming system, typically an engine such as a diesel engine, on
an emulsified fuel formulation containing the component, typically by
introducing the emulsified formulation into a combustion chamber of an
engine.

[0107]The oxygenate or where present, the emulsifier, may itself be
supplied as part of a mixture which is suitable for and/or intended for
use as a fuel additive.

[0108]Components (a) to (c) may be blended together in accordance with the
present invention described above, in particular with respect to the
emission reducing properties of the resultant fuel formulation. An
emulsifier is suitably also included in the formulation.

[0109]Components (a) to (c) may optionally be blended with one or more
additional components, for example fuel additives of the type described
above.

[0110]Another aspect of the present invention provides a method of
operating a fuel consuming system, which method involves introducing into
the system a fuel formulation according to the first aspect, and/or a
fuel formulation prepared according to the second aspect. Again the fuel
formulation may be introduced for one or more of the purposes described
above in connection with the sixth or seventh aspects of the present
invention, in particular to reduce combustion-related emissions from the
system.

[0111]The fuel consuming system may in particular be an engine, such as an
automotive engine, in which case the method may involve introducing the
fuel formulation into a combustion chamber of the engine. It may be an
internal combustion engine, and/or a vehicle which is driven by an
internal combustion engine. The engine is preferably a compression
ignition (diesel) engine. Such a diesel engine may be of the direct
injection type, for example of the rotary pump, in-line pump, unit pump,
electronic unit injector or common rail type, or of the indirect
injection type. It may be a heavy or a light duty diesel engine.

[0112]Engines of this type may produce improved results in particular in
relation to the reduction of combustion-related emissions if they further
comprise an exhaust after-treatment device, such as a catalytic converter
or diesel particulate filter. Such devices are suitably selected or set
up so as to reduce emissions from the particular formulation of the
present invention being used.

[0113]Thus, in another aspect, the present invention provides a vehicle
emissions control system comprising an engine adapted to run on a
formulation according to the first aspect, and an exhaust after-treatment
device adapted to remove emissions obtained from combustion of said
formulation in the engine.

[0114]Throughout the description and claims of this specification, the
words "comprise" and "contain" and variations of the words, for example
"comprising" and "comprises", mean "including but not limited to", and
are not intended to (and do not) exclude other moieties, additives,
components, integers or steps.

[0115]Throughout the description and claims of this specification, the
singular encompasses the plural unless the context otherwise requires. In
particular, where the indefinite article is used, the specification is to
be understood as contemplating plurality as well as singularity, unless
the context requires otherwise.

[0116]Preferred features of each aspect of the present invention may be as
described in connection with any of the other aspects.

[0117]Other features of the present invention will become apparent from
the following examples. Generally speaking the present invention extends
to any novel one, or any novel combination, of the features disclosed in
this specification (including any accompanying claims and drawings). Thus
features, integers, characteristics, compounds, chemical moieties or
groups described in conjunction with a particular aspect, embodiment or
example of the present invention are to be understood to be applicable to
any other aspect, embodiment or example described herein unless
incompatible therewith.

[0118]Moreover, unless stated otherwise, any feature disclosed herein may
be replaced by an alternative feature serving the same or a similar
purpose.

[0119]The following examples illustrate the preparation and properties of
fuel formulations in accordance with the present invention.

EXAMPLE 1

[0120]A series of emulsion blends were made from mixtures of water and GTL
Fuel incorporating 5 or 10% of several different biocomponents that are
typically used in the fuel market. GTL fuel was sourced from the Shell
plant in Bintulu, Malaysia and had key physical properties as set out in
Table 1 below. The POME and RME were obtained from commercial sources.

[0121]The emulsions were made using a two-component emulsifier formula by
vigorous agitation of the fluids using a Silverson high shear mixer.
De-ionised water was added dropwise over a period of one minute and the
mixture was agitated for a further 1 minute to ensure complete mixing.

[0122]The resultant emulsions, details of which are shown in Table 2, were
decanted into measuring cylinders and the degree of separation was
monitored regularly over a period of one week. The results are shown in
Table 3.

where S indicates stable with no visible separation at all;SS indicates
some separation with some visible sediment or clearing of emulsion at the
top; andNS indicates not stable with complete phase separation.

[0123]The results show that formulations in accordance with the present
invention may be stable for useful periods of time. In particular, it is
apparent that it is possible to make emulsions that are stable for
several days or more with the fatty acid methyl esters in the 20% water
case and in other cases, the emulsions were stable for up to 2 days. 2
days is considered to be a reasonable criterion for emulsions to be
useable in an automotive fuel.